Request for Payment of Underpaid Tax: SDLT12/12A Process Explained

HMRC requests for underpaid SDLT: forms SDLT12, SDLT12A and SDLT13

When HMRC’s system shows that less Stamp Duty Land Tax has been paid than the amount stated on the SDLT return, it follows an automated collection process. HMRC first asks for the shortfall, then sends a reminder, and if payment is still not made, it moves the case into formal debt recovery. These forms do not by themselves decide a legal dispute about the correct tax; they mainly show that HMRC’s records treat an amount as unpaid.

• SDLT12 is HMRC’s first request for payment of the underpaid SDLT and normally includes a payslip.
• SDLT12A is an automatic reminder sent if the amount is not paid within the time allowed.
• SDLT13 warns that debt recovery action will start and that the case will be passed to HMRC Debt Management & Banking.
• These forms are part of an administrative, system-driven process based on the taxpayer’s own SDLT self-assessment.
• If you receive one, check the filed return, the amount and timing of payment, and whether the payment was matched and allocated correctly.
• The issue may be a real unpaid balance, a payment allocation problem, or a dispute about the correct SDLT liability, so the notice should not be ignored.

Scroll down for the full analysis.

HMRC requests for underpaid SDLT: what forms SDLT12, SDLT12A and SDLT13 mean

This page explains what happens when HMRC’s SDLT system decides that too little Stamp Duty Land Tax has been paid compared with the taxpayer’s own SDLT return. The source material is about HMRC’s processing steps: first asking for the shortfall, then sending a reminder, and then moving the debt into formal recovery.

What this rule is about

SDLT is generally filed and paid on a self-assessment basis. That means the taxpayer submits a return and states how much tax is due. HMRC’s systems then process that return. If the system identifies an underpayment by reference to that self-assessment, HMRC issues standard forms asking for the unpaid amount.

The point of this process is administrative rather than interpretative. It is not mainly about deciding a difficult legal question. It is about what HMRC does when its records show that the amount paid does not match the amount the return says is due.

What the official source says

The official material says that where the system calculates there is an underpayment of tax by reference to the taxpayer’s self-assessment, HMRC issues form SDLT12 at the appropriate time to request payment of the amount owed. That form includes a payslip.

If payment is not made within the time allowed by the system, HMRC automatically issues reminder form SDLT12A.

If payment is still not received, HMRC issues form SDLT13. This tells the purchaser or agent that action will begin for recovery of the debt by Debt Management & Banking. The system then automatically passes the debt details to that office.

What this means in practice

In practical terms, these forms are part of HMRC’s debt collection process for SDLT that HMRC believes is unpaid.

The sequence is:

• SDLT12: initial request for payment of the underpaid amount
• SDLT12A: reminder if payment is not made in time
• SDLT13: warning that debt recovery action will start, followed by referral to Debt Management & Banking

This matters because once the case reaches the debt management stage, the issue is no longer just an outstanding payment request. It becomes a recoverable tax debt in HMRC’s systems.

The source material does not set out any appeal rights, review process, or substantive legal test on this page. It simply describes the automated processing steps. So if a taxpayer or agent receives one of these forms, an important practical question is whether the issue is:

• a genuine failure to pay tax that the return itself shows is due, or
• a disagreement about what the correct SDLT liability should have been in the first place, or
• an administrative mismatch, such as payment not being allocated correctly

The page does not resolve those issues, but it shows that HMRC’s system will continue to escalate unless the underpayment is dealt with.

How to analyse it

If you receive one of these forms, a sensible way to analyse the position is:

• Check the SDLT return that was filed. What tax was self-assessed as due?
• Check what amount was actually paid, and when.
• Check whether HMRC may be comparing the return against a lower payment than was in fact made.
• Check whether the payment reference and allocation were correct.
• Check whether the issue is really about an unpaid balance, or whether it reflects a dispute about the correct amount of SDLT.
• If an agent is involved, confirm whether HMRC’s notice has gone to the purchaser, the agent, or both.

The source refers to the purchaser or agent being notified at the SDLT13 stage. That is a reminder that communications may involve either or both, depending on HMRC’s records.

Where the underpayment is real and undisputed, the practical effect of the forms is straightforward: HMRC is asking for payment and will escalate to debt recovery if payment is not made.

Example

Illustration: a purchaser files an SDLT return showing tax of £10,000 but only £8,000 is recorded by HMRC as paid. HMRC’s system treats the £2,000 difference as an underpayment by reference to the purchaser’s own self-assessment. It issues form SDLT12 asking for the £2,000. If that is not paid within the system’s time limit, form SDLT12A is sent as a reminder. If payment is still not received, form SDLT13 is issued and the debt is passed to Debt Management & Banking for recovery action.

Why this can be difficult in practice

The source material is brief and procedural. It does not explain why the underpayment has arisen. In real cases, that can matter a great deal.

For example, an apparent underpayment may result from:

• a simple failure to pay the full amount
• a payment made late
• a payment made but not matched correctly to the return
• a disagreement about the self-assessed liability

This page does not say how HMRC distinguishes between those situations before the forms are issued. It suggests the process is system-driven. That means a taxpayer or agent should not assume that receipt of the form settles the underlying legal position. But equally, they should not ignore it, because the system will continue into debt recovery if the matter is not resolved.

Key takeaways

• These forms are part of HMRC’s automated process for collecting SDLT that its system shows as underpaid.
• SDLT12 is the first payment request, SDLT12A is the reminder, and SDLT13 signals referral for debt recovery.
• The key practical step is to check whether there is a real unpaid balance or an administrative or substantive issue behind HMRC’s calculation.

This page was last updated on 24 March 2026

Useful article? You may find it helpful to read the original guidance here: Request for Payment of Underpaid Tax: SDLT12/12A Process Explained

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